Quantifying atrial anatomy uncertainty from clinical data and its impact on electro-physiology simulation predictions.

Patient-specific computational models of structure and function are increasingly being used to diagnose disease and predict how a patient will respond to therapy. Models of anatomy are often derived after segmentation of clinical images or from mapping systems which are affected by image artefacts, resolution and contrast. Quantifying the impact of uncertain anatomy on model predictions is important, as models are increasingly used in clinical practice where decisions need to be made regardless of image quality. We use a Bayesian probabilistic approach to estimate the anatomy and to quantify the uncertainty about the shape of the left atrium derived from Cardiac Magnetic Resonance images. We show that we can quantify uncertain shape, encode uncertainty about the left atrial shape due to imaging artefacts, and quantify the effect of uncertain shape on simulations of left atrial activation times.

Use of Intracardiac Echocardiography in Interventional Cardiology: Working With the Anatomy Rather Than Fighting It.

The indications for catheter-based structural and electrophysiological procedures have recently expanded to more complex scenarios, in which an accurate definition of the variable individual cardiac anatomy is key to obtain optimal results. Intracardiac echocardiography (ICE) is a unique imaging modality able to provide high-resolution real-time visualization of cardiac structures, continuous monitoring of catheter location within the heart, and early recognition of procedural complications, such as pericardial effusion or thrombus formation. Additional benefits are excellent patient tolerance, reduction of fluoroscopy time, and lack of need for general anesthesia or a second operator. For these reasons, ICE has largely replaced transesophageal echocardiography as ideal imaging modality for guiding certain procedures, such as atrial septal defect closure and catheter ablation of cardiac arrhythmias, and has an emerging role in others, including mitral valvuloplasty, transcatheter aortic valve replacement, and left atrial appendage closure. In electrophysiology procedures, ICE allows integration of real-time images with electroanatomic maps; it has a role in assessment of arrhythmogenic substrate, and it is particularly useful for mapping structures that are not visualized by fluoroscopy, such as the interatrial or interventricular septum, papillary muscles, and intracavitary muscular ridges. Most recently, a three-dimensional (3D) volumetric ICE system has also been developed, with potential for greater anatomic information and a promising role in structural interventions. In this state-of-the-art review, we provide guidance on how to conduct a comprehensive ICE survey and summarize the main applications of ICE in a variety of structural and electrophysiology procedures.

Semi-supervised clustering of fractionated electrograms for electroanatomical atrial mapping.

BACKGROUND: Electrogram-guided ablation procedures have been proposed as an alternative strategy consisting of either mapping and ablating focal sources or targeting complex fractionated electrograms in atrial fibrillation (AF). However, the incomplete understanding of the mechanism of AF makes difficult the decision of detecting the target sites. To date, feature extraction from electrograms is carried out mostly based on the time-domain morphology analysis and non-linear features. However, their combination has been reported to achieve better performance. Besides, most of the inferring approaches applied for identifying the levels of fractionation are supervised, which lack of an objective description of fractionation. This aspect complicates their application on EGM-guided ablation procedures. METHODS: This work proposes a semi-supervised clustering method of four levels of fractionation. In particular, we make use of the spectral clustering that groups a set of widely used features extracted from atrial electrograms. We also introduce a new atrial-deflection-based feature to quantify the fractionated activity. Further, based on the sequential forward selection, we find the optimal subset that provides the highest performance in terms of the cluster validation. The method is tested on external validation of a labeled database. The generalization ability of the proposed training approach is tested to aid semi-supervised learning on unlabeled dataset associated with anatomical information recorded from three patients. RESULTS: A joint set of four extracted features, based on two time-domain morphology analysis and two non-linear dynamics, are selected. To discriminate between four considered levels of fractionation, validation on a labeled database performs a suitable accuracy (77.6 %). Results show a congruence value of internal validation index among tested patients that is enough to reconstruct the patterns over the atria to located critical sites with the benefit of avoiding previous manual classification of AF types. CONCLUSIONS: To the best knowledge of the authors, this is the first work reporting semi-supervised clustering for distinguishing patterns in fractionated electrograms. The proposed methodology provides high performance for the detection of unknown patterns associated with critical EGM morphologies. Particularly, obtained results of semi-supervised training show the advantage of demanding fewer labeled data and less training time without significantly compromising accuracy. This paper introduces a new method, providing an objective scheme that enables electro-physiologist to recognize the diverse EGM morphologies reliably.

Automatic segmentation of the left atrium from MR images via variational region growing with a moments-based shape prior.

The planning and evaluation of left atrial ablation procedures are commonly based on the segmentation of the left atrium, which is a challenging task due to large anatomical variations. In this paper, we propose an automatic approach for segmenting the left atrium from magnetic resonance imagery. The segmentation problem is formulated as a problem in variational region growing. In particular, the method starts locally by searching for a seed region of the left atrium from an MR slice. A global constraint is imposed by applying a shape prior to the left atrium represented by Zernike moments. The overall growing process is guided by the robust statistics of intensities from the seed region along with the shape prior to capture the entire atrial region. The robustness and accuracy of our approach are demonstrated by experimental results from 64 human MR images.

Ethanol infusion in the vein of Marshall facilitates mitral isthmus ablation.

BACKGROUND: Treatment of perimitral flutter (PMF) requires bidirectional mitral isthmus (MI) block, which can be difficult with radiofrequency ablation (RFA). The vein of Marshall (VOM) is located within the MI. OBJECTIVE: To test whether VOM ethanol infusion could help achieve MI block. METHODS: Perimitral conduction was studied in patients undergoing ablation of atrial fibrillation. Group 1 included 50 patients with a previous atrial fibrillation ablation undergoing repeat ablation, 30 of whom had had MI ablation. Spontaneous (8 of 50) or inducible PMF (21 of 50) was confirmed by activation mapping. Group 2 included 21 patients undergoing de novo VOM ethanol infusion. The VOM was cannulated with a quadripolar catheter for pacing and with an angioplasty balloon to deliver up to four 1-mL infusions of 98% ethanol. Voltage maps were created before and after VOM ethanol infusion. Bidirectional MI block was verified by differential pacing. RFA times required to achieve it were assessed. RESULTS: In group 1, VOM ethanol infusion acutely terminated PMF in 5 of 29 patients. RFA needed to achieve bidirectional MI block was 2.2 ± 1.6 minutes. Presence of PMF or previous MI ablation did not affect RFA times. In group 2, RFA needed to achieve bidirectional MI block was 2.0 ± 1.6 minutes (P = NS). Five patients had bidirectional MI block achieved solely by VOM ethanol infusion without RFA. In both groups, ablation after VOM ethanol infusion was required in the annular aspect of the MI. There were no acute complications. CONCLUSION: VOM ethanol infusion is useful in the treatment of PMF and assists in reliably achieving bidirectional MI block.

Rapid high resolution electroanatomical mapping: evaluation of a new system in a canine atrial linear lesion model.

BACKGROUND: A canine right atrial (RA) linear lesion model was used to produce a complex pattern of RA activation to evaluate a novel mapping system for rapid, high resolution (HR) electroanatomical mapping. METHODS AND RESULTS: The mapping system (Rhythmia Medical, Incorporated) uses an 8F deflectable catheter with a minibasket (1.8 cm diameter), containing 8 splines of 8 electrodes (total 64 electrodes, 2.5 mm spacing). The system automatically acquires electrograms and location information based on electrogram stability and respiration phase. In 10 anesthetized dogs, HR-RA map was obtained by maneuvering the minibasket catheter during sinus rhythm and coronary sinus pacing. A right thoracotomy was performed, and either 1 or 2 (to create a gap) epicardial linear lesions were created on the RA free wall (surgical incision or epicardial radiofrequency lesions). RA maps during RA pacing close to the linear lesions were obtained. A total of 73 maps were created, with 44 to 729 (median 237) beats and 833 to 12 412 (median 3589) electrograms (≤2 to ≤5 mm from surface geometry), resolution 1.8 to 5.3 (median 2.7) mm, and 2.6 to 26.3 (median 7.3) minutes mapping time. Without manual annotation, the system accurately created RA geometry and demonstrated RA activation, identifying the location of lines of block and presence or absence of a gap in all 10 dogs. Endocardial radiofrequency catheter ablation of a gap (guided by activation map) produced complete block across the gap in all 3 dogs tested. CONCLUSIONS: The new HR mapping system accurately and quickly identifies geometry and complex patterns of activation in the canine RA, with little or no manual annotation of activation time.

Accuracy of left atrial anatomical maps acquired with a multielectrode catheter during catheter ablation for atrial fibrillation.

INTRODUCTION: Left atrial geometry provided by preprocedural MRI/CT imaging studies is often used to guide pulmonary vein isolation. Rapid 3D reconstruction of the left atrium (LA) can be obtained using multielectrode catheters in conjunction with electro-anatomical mapping (EAM) and can also be used to guide ablation. The objective of this study is to assess the accuracy of electro-anatomical left atrial maps acquired with the multispine catheter by comparing them to CT and MRI images. METHODS: Forty patients undergoing ablation for atrial fibrillation were studied. All patients underwent preprocedural CT/MRI imaging. 3D reconstructions of the LA were obtained using a multispine catheter with the Ensite/NavX mapping system. The operator was blinded to the results of the preprocedural imaging studies while acquiring the LA maps. RESULTS: Mean map acquisition time was 10.3 ± 3.0 min. There was a strong correlation between maximum pulmonary vein (PV) ostial length and intervein distances measured on the electro-anatomical maps and on the CT/MRI images. Moreover, 11 patients had right middle PVs which were detected during map acquisition. Six out of nine (67%) early branches of the right inferior PV and three out of three (100%) early branches of right superior PV were also identified. In two patients, one branch of the left superior PV and one branch of the left inferior PV were not detected during mapping. CONCLUSION: Left atrial anatomical maps acquired using multielectrode catheters in conjunction with EAM are accurate and provide information regarding pulmonary vein dimensions and geometry which is similar to that obtained with CT/MR imaging.

Complete antral encirclement is not required for pulmonary vein isolation.

BACKGROUND: Complete circumferential antral ablation may not be necessary for successful pulmonary vein (PV) isolation in patients with paroxysmal atrial fibrillation (AF). OBJECTIVE: We examined the feasibility of a noncircumferential approach limited to segments of the antra required for PV-atrial conduction. METHODS: During ablation for paroxysmal AF, each PV antrum was divided into six segments, and ablation was sequentially targeted to antral segments with the earliest activity until bidirectional isolation was achieved. Ablation at the ostium was avoided. Patients requiring complete circumferential ablation (circumferential group) were compared with those undergoing incomplete antral ablation (noncircumferential group) with respect to freedom from symptomatic atrial arrhythmia, procedure, and ablation times. RESULTS: Ninety-nine patients underwent ablation with successful isolation of PVs (n = 37 circumferential; n = 62 noncircumferential). There were no significant differences in age, gender, AF duration, or LA size. Procedure time (202 ± 45 vs. 185 ± 47 minutes; P = .06) and ablation time (51 ± 15 vs. 41 ± 14 minutes; P = .004) were shorter in the noncircumferential group. During follow-up (12 ± 6 months), freedom from symptomatic recurrence was 73% in both groups (P = .97), with organized atrial tachycardia being more common in the circumferential group (P = .06). In 22 patients undergoing repeat study, PV reconnection was demonstrated in 82% and 81% of PVs in each group. Reconnection in the noncircumferential group occurred in previously ablated segments in 10 (77%) of 13 cases. CONCLUSIONS: Noncircumferential antral ablation achieves similar success rates with shorter procedure and ablation times than circumferential ablation. Greater attention should be focused on producing permanent lesions rather than on completing antral encirclement after isolation is achieved.

Influence of different doses of retinoic acid on cardiac remodeling.

OBJECTIVE: The role of retinoic acid in promoting postnatal heart alterations is still unclear. The aim of this study was to evaluate whether the cardiac alterations caused by all-trans- retinoic acid (ATRA) in normal adult rat hearts are physiologic or pathologic and if these alterations are dose-dependent. METHODS: Rats were allocated into a control group that received a diet without ATRA (n=16), a group that received 0.3 mg of ATRA/kg of diet (n=17), a group that received a diet containing 10 mg of ATRA/kg (n=18), or a group that received 50 mg of ATRA/kg in the diet (n=18). After 4 wk, the animals were evaluated echocardiographically, morphologically, and biochemically. RESULTS: The 50-mg ATRA group presented cardiac hypertrophy with maintenance of cardiac geometry and increased systolic function, whereas diastolic function was similar to that of the control group. In addition, progressive increases in the ATRA dose resulted in gradual augmentations of left atrial diameter, left ventricular diastolic and systolic diameters, left ventricular mass index, cardiac output, cardiac index, and aortic velocity. The ATRA did not produce alterations in interferon-γ and tumor necrosis factor-α cardiac levels, interstitial collagen volume fraction, or the intensity and localization of connexin-43. In addition, no alteration was observed in ß-hydroxyacyl coenzyme A dehydrogenase, lactate dehydrogenase, or citrate synthase, suggesting that cardiac energetic metabolism was preserved with ATRA. CONCLUSION: These results suggest that ATRA produced dose-dependent effects and cardiac remodeling that is more compatible with a physiologic response.

Anatomy of right atrial structures by real-time 3D transesophageal echocardiography.

The rapid development of catheter ablation techniques for atrial arrhythmias has triggered a renewed interest in the anatomy of the right atrium. In particular, some atrial arrhythmias such as focal atrial arrhythmias or atrial flutter have been linked to the anatomic architecture of specific structures such as the crista terminalis or cavotricuspid isthmus. Real-time 3-dimensional transesophageal echocardiography (RT 3D TEE) is a recently developed technique that provides 3D images of unprecedented quality. Because the right atrium is very close to the transducer, this technique may provide high-quality images of those atrial structures involved in ablation procedures. This review describes a step-by-step approach for acquisition and processing of RT 3D TEE images of right atrial structures of relevance to electrophysiologists. For anatomical correlations of RT 3D TEE images, selected images of right atrial structures were matched to anatomical specimens.

Complex fractionated electrograms and AF nests in vagally mediated atrial fibrillation.

BACKGROUND: Catheter ablation targeting of complex fractionated atrial electrograms (CFAEs) is one of the techniques used for atrial fibrillation (AF) ablation. The ablation of sites showing a high-frequency spectral component (HFC) during sinus rhythm, known as AF nests, has been introduced as an adjunct to conventional ablation. Known locations of some AF nests are similar to CFAE sites. However, it has not been systematically evaluated whether these two targets represent the same foci. The purpose of this study was to compare the anatomical locations of these sites using an animal model of vagally mediated AF. METHODS: Five anesthetized open-chest dogs were evaluated. Atrial electrograms were obtained epicardially. AF was induced by burst atrial pacing with 20 Hz during vagal stimulation. A total of 15 sites (eight sites in right atrium and seven sites in left atrium) were evaluated in each animal. The CFAE was determined during AF according to the electrogram patterns. After sinus conversion, real-time spectrum analysis was used for AF nest assessment at the same location. RESULTS: The CFAE was observed at the high and mid sulcus terminalis areas, pulmonary vein antrum, and mid portion of the coronary sinus. Among them, only 60% of the CFAE sites showed HFC during sinus rhythm. In addition, some of the non-CFAE sites (22%) showed HFC during sinus rhythm. CONCLUSION: The CFAE sites were not the same as the AF nests in this animal model of vagally mediated AF. Therefore, these two types of ablation methods appear to target different substrates of AF.

Anatomical pitfalls during encircling cryoablation of the left atrium for atrial fibrillation therapy in the pig.

We previously published encircling endocardial cryo-isolation of the pulmonary vein (PV) region. This study documented mechanisms of isolation failure using CARTO mapping. Cryo-isolation used a modified Surgifrost introduced via a Universal Cardiac Introducer on the left atrial appendage. Of five pigs, two had incomplete isolation and repeat mapping: Activation was over Bachmann's bundle (BB) in one and the coronary sinus (CS) in the other. Repeat cryoablation failed to eliminate gaps. Histologically, the BB gap had nonlesioned sub-epicardial fibres and thick fat covering the cryolesioned BB: fat protecting the epicardium from cryoablation. The inferior gap had a large CS, and a thick myocardium bridging the isthmus: myocardial thickness and CS thermal sink preventing transmural cryolesions. CARTO mapping localized gaps. Although the CS is known to cause failure, its protective mechanism is not well documented. The BB gap is novel. These findings have important clinical implications for isolation of the PV region.

Internal atrial shock delivery by standard diagnostic electrophysiology catheters in goats: effects on atrial electrogram amplitude and tissue architecture.

AIMS: In this study, we evaluated the effects of atrial shock delivered via diagnostic electrophysiology catheters. METHODS AND RESULTS: In 11 anaesthetized goats, decapolar catheters were positioned in the right atrial appendage (RAA) and coronary sinus (CS). Three different catheters and two cardioversion protocols were evaluated. In four goats, 50 J shocks were delivered using catheters with 1 mm electrodes (surface area 70 mm(2)). In 6 goats, catheters with 2 mm electrodes (area 140 mm(2)) were used. In three of the six goats, 50 J shocks were given while in the other 3, 10 J shocks were delivered. In 1 goat 50 J shocks were delivered via 5 mm electrode catheters (area 310 mm(2)). No persisting adverse effects occurred. However, the electrogram amplitude at the RAA and CS decreased by >50-98% (P > 0.01). The amount of amplitude decrease was most pronounced at the CS site and for 50 J shocks. Goats were sacrificed after 9 +/- 1 days. Macroscopy revealed endocardial lesions at the electrode locations. Microscopy showed endocardial thrombosis, and necrosis with formation of granulation tissue. Changes were most marked with diagnostic catheters and 50 J shocks. CONCLUSIONS: Atrial shock delivery via diagnostic catheters causes local ablation lesions. The amount of amplitude decrease, macroscopic and microscopic damages were related to the energy applied and electrode surface area.

Registration of 3D computed tomographic images with interventional systems: implications for catheter ablation of atrial fibrillation.

Despite the great promise catheter ablation offers in the treatment of complex arrhythmias such as atrial fibrillation (AF), long procedure times and somewhat suboptimal results hinder the widespread use of this technique. As fluoroscopy does not provide contrast differentiation between the area of interest and the surrounding structures, there is a lack of proper intra procedure image guidance. Segmentation of anatomical structures such as the left atrium (LA) can be performed using images obtained with modalities such as computed tomography (CT). However, unlike the cardiac mapping systems, these imaging systems do not track catheters in real time. This review addresses the evolving concept of image registration to deliver therapy in cardiac arrhythmias.

Registration of three-dimensional left atrial computed tomographic images with projection images obtained using fluoroscopy.

BACKGROUND: Anatomic structures such as the left atrium and the pulmonary veins (PVs) are not delineated by fluoroscopy because there is no contrast differentiation between them and the surrounding anatomy. Representation of an anatomic structure via a 3D model obtained from computed tomography (CT) imaging and subsequent projection of these images over the fluoroscopy system may help in navigation of the mapping and ablation catheter to the appropriate sites during electrophysiology procedures. METHODS AND RESULTS: In this feasibility study, in vitro experiments were performed with a plastic heart model (phantom) with 2 catheters or radiopaque platinum beads placed in the phantom at the time of CT imaging and fluoroscopy. Subsequently, 20 consecutive patients underwent contrast-enhanced, ECG-gated CT scanning. Left atrial volumes were generated from the reconstructed data at &75% of the R-R interval during the cardiac cycle. Similarly, the superior vena cava and the coronary sinus were also reconstructed from these images. During the electrophysiology procedure, digital records (cine sequences) were obtained. Using predetermined algorithms, both the phantom model and the patients' 3D left atrial models derived from the CT were registered with projection images of fluoroscopy. Registration was performed with a transformation that linked the superior vena cava and the coronary sinus from the CT model with a catheter placed inside the coronary sinus via the superior vena cava. Registration was successfully accomplished with the plastic phantom and in all 20 patients. Registration accuracy was assessed in the phantom by assessing the overlapping beads seen both in the CT and the fluoroscopy images. The mean registration error was 1.4 mm (range 0.9 to 2.3 mm). Accuracy of the registered images was assessed in patients with recordings from a basket catheter placed sequentially in the superior PVs and by injecting contrast into the PVs to assess overlapping of contrast-filled PVs with the corresponding vessels on the registered images. The images could be calibrated quite accurately. Any rotational error, which was usually minor, could be corrected by rotating the images as needed. CONCLUSIONS: Registration of 3D models of the left atrium and PVs with fluoroscopic images of the same is feasible and could enable appropriate navigation and localization of the mapping and ablation catheter during procedures such as atrial fibrillation ablation.

Intracardiac echocardiographic anatomy for the interventional electrophysiologist.

The development of intracardiac echo has led to an increasing appreciation of the important relationship between arrhythmia mechanism and anatomy. This review describes the anatomic structures involved in arrhythmia mechanism that may be imaged with ICE and the use of intracardiac echo to guide mapping and ablation.

Feasibility and validation of registration of three-dimensional left atrial models derived from computed tomography with a noncontact cardiac mapping system.

OBJECTIVES: The purpose of this study was to determine the feasibility and assess the validity of registering three-dimensional (3D) models from computed tomographic (CT) images using a cardiac mapping system. BACKGROUND: Registration of 3D anatomic models with an interventional system could help identify and navigate mapping and ablation catheters over a complex structure such as the left atrium (LA). METHODS: ECG-gated, contrast-enhanced cardiac CT imaging was performed in 14 patients with atrial fibrillation. Segmentation was used to create 3D models of the LA. The 3D models were registered with the mapping system using a series of fiducial points. Registration was accomplished retrospectively in the first 10 patients, and catheter navigation was visualized from recorded data. In the final four patients, registration was accomplished in real time during electrophysiologic study. The mapping catheter position, as it was navigated inside the LA, was applied to the registered model in real time. For the validation study, temporary pacing leads were implanted in the LA of 10 dogs. Following this, CT scanning, segmentation, LA model importation, and registration was described previously. After registration, a mapping catheter was positioned at the site of each buried lead according to the registered model with no fluoroscopic guidance. A radiofrequency lesion was created at this location, and the dog was sacrificed, the heart removed and stained, and the distance between the buried lead and the lesion measured. RESULTS: During the feasibility study, the location of the catheter in the registered model correlated with fluoroscopy, angiography, and intracardiac electrograms. LA endocardial potentials during sinus rhythm and any premature atrial contractions also were successfully delineated over the registered models. In the validation study, the mean target registration error was 2.0 +/- 3.6 mm. CONCLUSIONS: Registration of CT-derived 3D models of the LA using a cardiac mapping system is feasible and accurate.

Relationship between anatomic location of the crista terminalis and double potentials recorded during atrial flutter: intracardiac echocardiographic analysis.

INTRODUCTION: The activation sequence in typical atrial flutter (AFL) around the tricuspid annulus is well described. However, activation of the remainder of the right atrium (RA) is not well defined. Previous studies have shown a linear block at the crista terminalis (CT) during AFL. The aim of this study was to evaluate the relationship between the location of the CT and the line of block by intracardiac echocardiography (ICE). METHODS AND RESULTS: Twenty-one patients with typical AFL were included in the study. The ICE imaging catheter (9-French with 9-MHz ultrasound transducer) was advanced to the RA. Under ICE guidance, a 20-pole roving catheter was used to map double potentials (DPs) during AFL, and three-dimensional images of the RA were reconstructed. During counterclockwise (CCW), clockwise (CW) AFL, or both, a line of conduction block manifested by DPs was identified at a septal site adjacent to the CT in 12 patients and in the posteroseptal RA in 9 patients. CONCLUSION: The functional line of block in CCW and CW AFL is localized not at the CT but at the septal edge of the CT or in the posteroseptal RA.

Intrapericardial echocardiography: a novel catheter-based approach to cardiac imaging.

BACKGROUND: Transvascular catheter-based intracardiac echocardiography has been successfully used to help guide catheter ablation and electrophysiologic procedures. It has recently been demonstrated that catheters can be safely placed into the pericardial space to allow for epicardial cardiac mapping and ablation. We evaluated the feasibility of catheter-based intrapericardial echocardiography (IPE) during such procedures to identify cardiac structures and visualize intracardiac catheters. METHODS: IPE was performed in 7 goats by placing a phased-array ultrasound transducer contained within a 10F steerable catheter into the pericardial space using the same transthoracic subxyphoid approach as used to map and ablate epicardial ventricular tachycardia. Images were obtained of cardiac structures and of intracardiac ablation catheters. After the procedure, the hearts were harvested to assess for possible IPE-related lesions. RESULTS: The IPE catheter could be easily placed inside the pericardial space in all animals. In 7 of 7 cases, longitudinal and short-axis views of right- and left-sided chambers and valves were obtained, similar in orientation to transesophageal echocardiography. Visualization of atrial appendages (6/7), pulmonary veins (6/7), coronary arteries (6/7), and coronary sinus (3/6) was also feasible. Assessment of intracardiac transvalvar and venous blood flow was achieved by spectral and color Doppler. The ablation catheter could be clearly visualized inside cardiac chambers. No arrhythmias were induced with IPE catheter manipulation. After harvesting the hearts, no lesions resulting from the procedure were observed. CONCLUSION: In this experimental setting, IPE was able to provide detailed images of cardiac structures and establish the relative position of the ablation catheter.